Viral variants and methods for detecting same

ABSTRACT

The present invention relates generally to viral variants exhibiting reduced sensitivity to particular agents and/or reduced interactivity with immunological reagents. More particularly the present invention is directed to hepatitis B variants exhibiting complete or partial resistance to nucleoside analogues and/or reduced interactivity with antibodies to viral surface components. The present invention further contemplates assays for detecting such viral variants which assays are useful in monitoring anti-viral therapeutic regimes.

[0001] The present invention relates generally to viral variants exhibiting reduced sensitivity to particular agents and/or reduced interactivity with immunological reagents. More particularly, the present invention is directed to hepatitis B variants exhibiting complete or partial resistance to nucleoside analogues and/or reduced interactivity with antibodies to viral surface components. The present invention further contemplates assays for detecting such viral variants which assays are useful in monitoring anti-viral therapeutic regimes.

[0002] Bibliographic details of the publications numerically referred to in this specification are collected at the end of the description. Sequence Identity Numbers (SEQ ID NOs.) for the nucleotide and amino acid sequences referred to in the specification are defined following the bibliography.

[0003] Throughout this specification, unless the context requires otherwise, the word “comprise” or variations such as “conprises” or “comprising” or the term “includes” or variations thereof, will be understood to imply the inclusion of a stated element or integer or group of elements or integers but not the exclusion of any other element or integer or group of elements or integers. In this regard, in construing the claim scope, an embodiment where one or more features is added to any of claim is to be regarded as within the scope of the invention given that the essential features of the invention as claimed are included in such an embodiment.

[0004] Specific mutations in an amino acid sequence are represented herein as “Xaa₁nXaa₂” where Xaa₁ is the original amino acid residue before mutation, n is the residue number and Xaa₂ is the mutant amino acid. The abbreviation “Xaa” may be the three letter or single letter amino acid code. The amino acid residues for Hepatitis B virus DNA polymerase are numbered with the residue methionine in the motif Tyr Met Asp Asp (YMDD) being residue number 550. In the priority document, Australian Patent Application No. PO3519, filed Nov. 8, 1996, the same methionine was designated residue 530. The amino acid residues for the DNA polymerase referred to in this specification have been re-numbered accordingly.

[0005] Hepatitis B Virus (HBV) can cause debilitating disease conditions and can lead to acute liver failure. HBV is a DNA virus which replicates via an RNA intermediate and utilizes reverse transcription in its replication strategy (1). The HBV genome is of a complex nature having a partially double stranded DNA structure with overlapping open reading frames encoding surface, core, polymerase and X genes. The complex nature of the HBV genome is represented in FIG. 1.

[0006] The presence of an HBV DNA polymerase has led to the proposition that nucleoside analogues could act as effective anti-viral agents. Examples of nucleoside analogues currently being tested are penciclovir and its oral form famciclovir (2, 3, 4, 5) and lamivudine (6,7). There is potential for such agents to be used in the treatment of chronic HBV infection.

[0007] Peniciclovir has been recently shown to have potent inhibitory activity against duck HBV DNA synthesis in vitro and has been shown to inhibit HBV DNA polymerase-reverse transcriptase activity in vitro (8,9). Similarly, oral famiciclovir has been demonstrated to inhibit intra-hepatic replication of duck HBV virus in vivo (10). In man, famciclovir has been shown to reduce HBV DNA replication in a patient with severe hepatitis B following orthotopic liver transplantation (OLT) (11).

[0008] In work leading up to the present invention, nucleoside analogue antiviral therapy was used to control severe post-OLT recurrence of HBV infection (12). Long term therapy is mandatory where patients are immunosuppressed and the rate of HBV replication is very high. However, under such conditions, as with any long term chemotherapy of infectious agents, there is a potential for development of resistance or reduced sensitivity to the therapeutic agents employed.

[0009] In accordance with the present invention, the inventors have identified variants of HBV with mutations in the HBV DNA polymerase gene which to varying extents reduce the sensitivity of HBV to nucleoside analogues. The identification of these HBV variants is important for the development of assays to monitor nucleoside analogue therapeutic regimes and to screen for agents which can mask the effects of the mutation. In addition, since the HBV genome comprises a series of overlapping open reading frames, a nucleotide mutation in one open reading frame can affect translation products in another open reading frame. In further accordance with the present invention, the inventors have observed mutations which reduce the interactivity of immunological reagents, such as antibodies and immune cells, to viral surface components. Such viral variants are referred to herein as “escape mutants” since they potentially escape existing immunological memory.

[0010] Accordingly, one aspect of the present invention is directed to a variant of an isolated DNA virus which replicates via an RNA intermediate wherein said variant comprises a nucleotide mutation in a gene encoding a DNA polymerase resulting in at least one amino acid addition, substitution and/or deletion to said DNA polymerase.

[0011] Another aspect of the present invention provides a variant of an isolated DNA virus which replicates via an RNA intermediate wherein said variant comprises a nucleotide mutation in a gene encoding a viral surface component resulting in at least one amino acid addition, substitution and/or deletion in said viral surface component.

[0012] Still a further aspect of the present invention is directed to a variant of an isolated DNA virus which replicates via an RNA intermediate at least wherein said variant comprises a nucleotide mutation in an overlapping portion of at least two open reading frames resulting in an amino acid addition, substitution and/or deletion to translation products of said open reading frames.

[0013] Preferably, the DNA virus is a hepatitis virus or a related virus and is most preferably HBV.

[0014] A “related virus” in accordance with the present invention is one related at the genetic, immunological, epidemiological and/or biochemical levels.

[0015] Preferably, the mutation in the DNA polymerase results in decreased sensitivity of the HBV to a nucleoside analogue.

[0016] Preferably, the mutation in the viral surface component reduces the interactivity of immunological reagents such as antibodies and immune cells to the viral surface component.

[0017] Most preferably, the viral surface component is a viral surface antigen. The reduction in the interactivity of immunological reagents to a viral surface component generally includes the absence of immunological memory to recognise or substantially recognise the viral surface component.

[0018] A viral variant may, in accordance with a preferred aspect of the present invention, carry mutation only in the DNA polymerase or the surface antigen or may carry a mutation in both molecules. The term “mutation” is to be read in its broadest context and includes a silent mutation not substantially affecting the normal function of the DNA polymerase or surface antigen or may be an active mutation having the effect of inducing nucleoside analogue resistance or an escape mutant phenotype. Where multiple mutations occur in accordance with the present invention or where multiple phenotypes result from a single mutation, at least one mutation must be active or the virus must exhibit at least one altered phenotype such as nucleoside analogue resistance or reduced immunological interactivity to the surface antigen.

[0019] Regions of the HBV polymerase show amino acid similarity with other RNA-dependent DNA polymerases and RNA-dependent polymerases (13). In this specification, reference is made to the conserved regions defined by Poch et al (13) as domains B and C.

[0020] Preferably, the mutation results in an altered amino acid sequence in the B domain and/or C domain or regions proximal thereto of the HBV DNA polymerase. The present invention does not extend to a mutation alone in the YMDD motif of the C domain of the HBV DNA polymerase although such a mutation is contemplated by the present invention if it occurs in combination with one or more mutations in another location.

[0021] The mutation in the viral surface component is preferably in one or more amino acid residues within the major hydrophilic regions of the protein, in particular within the amino acid sequence 118-169 of the HBV viral surface antigen and also the regions from amino acids sequence 169 to 207 which are on the external surface of the protein.

[0022] According to a preferred aspect of the present invention, there is provided an HBV variant comprising a mutation in the nucleotide sequence encoding a DNA polymerase resulting in an amino acid addition, substitution and/or deletion in said DNA polymerase in its B domain and/or C domain or in a region proximal thereto, provided said mutation is not in the YMDD motif of the C domain alone, and wherein said variant exhibits decreased sensitivity to a nucleoside analogue.

[0023] Another preferred aspect of the present invention contemplates an HBV variant comprising a mutation in the nucleotide sequence encoding a viral surface component resulting in an amino acid addition, substitution and/or deletion in said viral surface component in a region corresponding to the B domain and/or C domain of HBV DNA polymerase or a region proximal to the B domain and/or C domain of HBV DNA polymerase and wherein said variant exhibits decreased interactivity of immunological reagents to said viral surface component.

[0024] Yet another preferred aspect of the present invention relates to an HBV variant comprising a mutation in the nucleotide sequence encoding a viral surface component resulting in an amino acid addition, substitution and/or addition in said viral surface component in a region defined by amino acids 118 to 169 and also 169 to 207 of the HBV surface antigen or functionally equivalent region wherein said variant exhibits decreased interactivity of immunological reagents to said viral surface component.

[0025] Still yet another aspect of the present invention is directed to an HBV variant comprising a mutation in an overlapping open reading frame in its genome wherein said mutation is in the B and/or C domain of DNA polymerase provided that it is not in the YMDD motif of the C domain alone; and in the overlapping region corresponding to amino acids 118 to 169 and also 169 to 207 or equivalent of HBV surface antigen and wherein said variant exhibits decreased sensitivity to a nucleotide analogue and exhibits decreased interactivity to immunological reagents specific to HBV surface antigens.

[0026] The viral variant exhibiting reduced interactivity to immunological reagents is an escape mutant since antibodies or other immunological response to HBV from a prior exposure to the virus or following vaccination are no longer effective in targeting a viral surface component since the mutation has altered a B- and/or T-cell epitope on the surface antigen.

[0027] The nucleoside analogues contemplated by the present invention include penciclovir and its oral form famciclovir as well as lamivudine (3TC). Different variants may be resistant to different nucleoside analogues. For example, in one embodiment, a variant in the B domain of HBV DNA polymerase may be resistant to famciclovir whereas a variant in the C domain may be resistant to 3TC.

[0028] The B domain is considered to comprise amino acid residues 505 to 529 of HBV DNA polymerase. This sequence is represented as follows:

[0029] S/A H PI I/V LGFRK I/L PMG V/G GLSPFLLAQF.

[0030] Reference to the B domain includes reference to proximal regions which includes up to about 20 amino acids on either side of the domain. Preferably, the mutation is in one or more of the following amino acids:

[0031] Q/K T Y/F G R/W KLHL Y/L S/A HPI I/V LGFRK I/L PMG V/G GLSPFLLAQFTSAI C/L S

[0032] The C domain comprises amino acids 546 to 556 as follows:

[0033] A/V F S/A YMDD V/L/M VLG

[0034] This includes the YMDD domain in which the methione residue is considered residue 550 (formally regarded as residue number 530). The residue numbering in this specification has been adjusted according to the new numbering system where the methione of YMDD is 550.

[0035] Reference to the C domain includes proximal regions of up to 20 amino acids either side of the domain.

[0036] The term “resistance” is used in its most general sense and includes total resistance or partial resistance or decreased sensitivity to a nucleoside analogue.

[0037] Preferably, the variants are in isolated form such that they have undergone at least one purification step away from naturally occurring body fluid. Alternatively, the variants may be maintained in isolated body fluid or may be in DNA form. The present invention also contemplates infectious molecular clones comprising the genome or parts thereof from a variant HBV.

[0038] Preferred mutations in the HBV DNA polymerase include one or more of Gly498Glu, Arg/Trp499Lys, Thr530Ser, Ile509Val, Phe512Leu, Val519Leu, Pro523Leu, Leu526Met, Ile533Leu, Met550Val/Ile and/or Ser559Thr. Preferred mutations in the HBV surface antigen include one or more of Asp144Glu and/or Gly145Arg. These correspond to positions 498 and 499 of DNA polymerase, respectively. More preferably, the variants contain two or more of the above-mentioned mutations.

[0039] One particular mutant HBV has the nucleotide sequence set forth in SEQ ID NO:17 and exhibits a multiphenotypic mutation rendering the DNA polymerase resistant to nucleoside analogues and an altered surface antigen such that it has reduced interactivity with antibodies to HBV surface antigen. The mutation is G498E in the DNA polymerase open reading frame as D144E and G145R in the surface antigen. This results from a double mutation in nucleotide numbers 226 and 227 of SEQ ID NO:17 to G and A. The polymerase protein of HBV is also similar to the DNA polymerase of Herpes Simplex Virus (HSV) (see FIG. 3 for alignment). A mutation (Gly841Cys) in the HSV polymerase gene was selected for in the presence of farrciclovir (15). This mutation occurs in the same position as the G498E mutation of the HBV polymerase.

[0040] The present invention extends to the nucleotide sequence set forth in SEQ ID NO:17 as well as a nucleotide sequence having at least 60% similarity thereto and which carries a double mutation in the amino acid sequence of DNA polymerase and the HBV surface antigen. Accordingly, the present invention is directed to an HBV having the nucleotide sequence as set forth in SEQ ID NO:17 or a derivative thereof having a single or multiple nucleotide addition, substitution and/or deletion thereto such as a nucleotide sequence having at least 60% similarity to SEQ ID NO:17. A derivative includes parts, fragments, portions and homologues of SEQ ID NO:17. This aspect of the present invention also extends to a nucleotide sequence capable of hybridizing under low stringency conditions at 42° C. to SEQ ID NO:17.

[0041] Reference herein to a low stringency at 42° C. includes and encompasses from at least about 1% v/v to at least about 15% v/v formamide and from at least about 1M to at least about 2M salt for hybridisation, and at least about 1M to at least about 2M salt for washing conditions. Alternative stringency conditions may be applied where necessary, such as medium stringency, which includes and encompasses from at least about 16% v/v to at least about 30% v/v formamide and from at least about 0.5M to at least about 0.9M salt for hybridisation, and at least about 0.5M to at least about 0.9M salt for washing conditions, or high stringency, which includes and encompasses from at least about 31% v/v to at least about 50% v/v formamide and from at least about 0.01M to at least about 0.15M salt for hybridisation, and at least about 0.01M to at least about 0.15M salt for washing conditions.

[0042] Accordingly, another aspect of the present invention contemplates a variant HBV exhibiting reduced sensitivity to a nucleoside analogue and reduced interactivity to an antibody to wild-type HBV surface antigen, said HBV variant characterised by one or more of the following characteristics:

[0043] (i) a nucleotide sequence of its genome as set forth in SEQ ID NO:17 or a sequence having at least 60% similarity thereto;

[0044] (ii) a nucleotide sequence capable of hybridising to SEQ ID NO:17 under low stringency conditions at 42° C.;

[0045] (iii) a mutation in an overlapping portion of open reading frames for DNA polymerization and HBV surface antigen; and

[0046] (iv) a mutation in the B and/or C domain of HBV DNA polymerase and is a region corresponding to amino acids 118 to 169 and also 169 to 207 of HBV surface antigen.

[0047] According to another aspect of the present invention, there is provided a variant HBV comprising a nucleotide sequence which encodes a DNA polymerase having the amino acid sequence:

[0048] X₁HPIX₂LGX₃RKX₄PMGX₅GLSX₆FLX₇AQFTSAX₈X₉ . . . X₁₀FX₁₁YX₁₂DDX₁₃VLGAX₁₄X₁₅

[0049] wherein

[0050] X₁ is S or A;

[0051] X₂ is I or V;

[0052] X₃ is F or L;

[0053] X₄ is I or L;

[0054] X₅ is L or V or G;

[0055] X₆ is P or L;

[0056] X₇ is L or M;

[0057] X₈ is I or L;

[0058] X₉ is C or L;

[0059] X₁₀ is A or V;

[0060] X₁₁ is S or A;

[0061] X₁₂ is M or I or V;

[0062] X₁₃ is V or L or M;

[0063] X₁₄ is K or R; and/or

[0064] X₁₅ S or T;

[0065] and wherein said variant exhibits reduced sensitivity to a nucleoside sensitivity to a nucleoside analogue, such as famciclovir (penciclovir) and/or lamivudine (3TC).

[0066] Another embodiment of the present invention is directed to a variant HBV comprising a nucleotide sequence which encodes a surface antigen having at least one amino acid substitution, addition and/or deletion to amino acid residue numbers 118 to 169 and also 169 to 207 of said surface antigen which corresponds to a DNA polymerase having the amino acid sequence:

[0067] X₁₆TX₁₇X₁₈X₁₉KLHLX₂₀X₂₁HPX₂₂LGX₃RKX₄PMGX₅GLSX₆FLX₇AQFTSAX₈X₉ . . . X₁₀FX₁₁YX₁₂DDX₁₃VLGAX₁₄X₁₅

[0068] wherein:

[0069] X₁₆ is Q or K;

[0070] X₁₇ is Y or F;

[0071] X₁₈ is G or E;

[0072] X₁₉ is R or W or K;

[0073] X₂₀ is Y or L;

[0074] X₂₁ is S or A;

[0075] X₂₂is I or V;

[0076] X₃ is F or L;

[0077] X₄ is I or L;

[0078] X₅ is L or V or G;

[0079] X₆is P or L;

[0080] X₇ is L or M;

[0081] X₈ is I or L;

[0082] X₉ is C or L;

[0083] X₁₀ is A or V;

[0084] X₁₁ is S or A;

[0085] X₁₂ is M or I or V;

[0086] X₁₃ is V or L or M;

[0087] X₁₄ is K or R; and/or

[0088] X₁₅ S or T;

[0089] and wherein said variant exhibits reduced interactivity with immunological reagents, such as an antibody, to said surface antigen.

[0090] Examples of preferred variants comprise the amino acid sequences shown in FIG. 4. An example of a particularly preferred mutant is shown in FIG. 5 (SEQ ID NO:17).

[0091] The identification of the variants of the present invention permits the generation of a range of assays to detect such variants. The detection of such variants may be important in identifying resistant variants to determine the appropriate form of chemotherapy and/or to monitor vaccination protocols.

[0092] Accordingly, another aspect of the present invention contemplates a method for determining the potential for an HBV to exhibit reduced sensitivity to a nucleoside analogue, said method comprising isolating DNA or corresponding mRNA from said HBV and screening for a mutation in the nucleotide sequence encoding HBV DNA polymerase resulting in at least one amino acid substitution, deletion and/or addition in the B domain or C domain or a region proximal thereto of said DNA polymerase wherein the presence of such a mutation is an indication of the likelihood of resistance to said nucleoside analogue.

[0093] A further aspect of the present invention provides a method for determining the potential for an HBV to exhibit reduced interactivity to antibody to HBV surface antigen, said method comprising isolating DNA or corresponding mRNA from said HBV and screening for a mutation in the nucleotide sequence encoding HBV surface antigen resulting in at least one amino acid substitution, deletion and/or addition in amino acids 118 to 169 and/or 169 to 207 of said surface antigen or a region proximal thereto of said surface antigen wherein the presence of such a mutation is an indication of the likelihood of reducing interactivity of said antibodies to said mutated surface antigen.

[0094] Preferably, the assay determines a mutation resulting in a Glu/Val519Leu substitution and/or a Leu526Met substitution and/or a Pro523Leu substitution and/or a S559T substitution, and/or Gly498Glu substitution, and/or Arg/Trp499Lys substitution.

[0095] The DNA or corresponding RNA may be assayed or alternatively the DNA polymerase or surface antigen may be screened for the mutation.

[0096] The detection according to this aspect of the invention may be any nucleic acid-based detection means, for example nucleic acid hybridisation techniques or polymerase chain reaction (PCR). The invention further encompasses the use of different assay formats of said nucleic acid-based detection means, including restriction fragment length polymorphism (RFLP), amplified fragment length polymorphism (AFLP), single-strand chain polymorphism (SSCP), amplification and mismatch detection (AMD), interspersed repetitive sequence polymerase chain reaction (IRS-PCR), inverse polymerase chain reaction (iPCR) and reverse transcription polymerase chain reaction (RT-PCR), amongst others.

[0097] The present invention extends to a range of immunologically based assays to detect variant HBV DNA polymerase or surface antigen. These assays are based on antibodies directed to naturally occurring HBV DNA polymerase or surface antigen which do not, or substantially do not, interact with the variant HBV DNA polymerase or surface antigen. Alternatively, antibodies to a variant HBV DNA polymerase or surface antigen are used which do not or substantially do not, interact with naturally occurring HBV DNA polymerase or surface antigen.

[0098] Monoclonal or polyclonal antibodies may be used although monoclonal antibodies are preferred as they can be produced in large quantity and in a homogenous form. A wide range of immunoassay techniques are available such as described in U.S. Pat. Nos. 4,016,043, 4,424,279 and 4,018,653.

[0099] The detection of amino acid variants of DNA polymerase is conveniently accomplished by reference to the consensus amino acid sequence shown in FIG. 4. The polymorphisms shown represent the variations shown in various data bases for active pathogenic HBV strains. Where an HBV variant comprises an amino acid different to what is represented, then such an isolate is considered a putative HBV variant having an altered DNA polymerase activity.

[0100] Accordingly, another aspect of the present invention contemplates a method for determining whether an HBV isolate encodes a variant DNA polymerase, said method comprising determining the amino acid sequence of its DNA polymerase directly or via a nucleotide sequence and comparing same to the amino acid sequence below:          DOMAIN A 421        430         440         450 S^(N) _(D)LSWLSLD VSAAFYH ^(I) _(P)PL HPAAMPHLL^(I) _(V) GSSGL^(S) _(D)RYVA 460           470             480           490 RLSS^(T) _(N)S^(R) _(N) ^(N) _(I)*N ^(N)Y_(H)Q^(H) _(Y) ^(G) _(R)***^(D) _(N)LH ^(D) _(N) ^(S) _(Y)CSR^(N) _(Q)LYVS L^(L) _(M)LLY^(K) _(Q)T^(Y) _(F)G^(R) _(W)                 DOMAIN B 500           510          520         530 KLHL^(Y)L ^(S) _(A)HPI^(I) _(V) LGFRK^(I) _(L)PMG^(V) _(G) GLSPFLLAQF TSAI^(C) _(L) ^(A) _(S) ^(V) _(M) ^(V) _(T) ^(R) _(C)R                DOMAIN C 540            550             560 AF^(F) _(P)HC^(L) _(V ^(A) VF^(S) AY MDD^(V)L MVLGA) ^(K) _(R) ^(S) _(T) ^(V) _(G) ^(Q) _(E)H^(L)S_(R)E^(S) _(F)L^(F) _(Y) ^(T) _(A) ^(A) _(S)               DOMAIN D         DOMAIN E 570              580         590          600 ^(V) _(I) ^(T) _(C) ^(N) _(S) ^(F) _(V)LL ^(S) _(D) ^(L) _(V)GI HLNP^(N) _(Q)KTKRW GYSLNFMGY^(V) _(I)I G

[0101] where the presence of a different amino acid from the consensus sequence indicates a putative HBV variant.

[0102] The present invention further contemplates agents which mask the nuclcoside analogue resistance mutation. Such agents will be particularly useful in long term treatment by nucleoside analogues. The agents may be DNA or RNA or proteinaceous or non-proteinaceous chemical molecules. Natural product screening such as from plants, coral and microorganisms is also contemplated as a useful potential source of masking agents. The agents may be in isolated form or in the form of a pharmaceutical composition and may be administered sequentially or simultaneously with the nucleoside analogue.

[0103] The subject invention extends to kits for assays for variant HBV. Such kits may, for example, contain the reagents from PCR or other nucleic acid hybridisation technology or reagents for immunologically based detection techniques.

[0104] The present invention is further described by the following non-limiting figures and examples.

[0105] In the figures:

[0106]FIG. 1 is a diagrammatic representation showing the partially double stranded DNA HBV genome showing the overlapping open reading frames encoding surface (S), core (C), polymerase (P) and X gene.

[0107]FIG. 2 is a graphical representation showing serum biochemical (ALT) and virological (HBV DNA) profile in the transplant patient and the responses following the introduction of various antiviral treatment programs. Treatment GCV+PFF, GCV and FCV[I] and FCV[II] are described in detail in the examples. Treatment GCV+PFF is ganciclovir plus foscarnet combination (12), treatment GCV is parenteral ganciclovir maintenance therapy and treatment FCV[I] and FCV[II] is oral famciclovir therapy at a dose of 250 mg or 500 mg twice daily, respectively. The day each therapy commenced is shown in brackets. The ALT (•-•) and the HBV DNA (□-□) responses are plotted against time from the commencement of antiviral therapy at 6 months post-OLT. The five key time points for the sequence analysis, pre-treatment (PRE-) and days 87, 600, 816 and 1329 post antiviral treatment are shown.

[0108]FIG. 3 is a representation showing amino acid alignment of the RNA dependent DNA polymerase sequence motifs from HBV, pre-treatment with famciclovir and 370 days post-treatment (total antiviral therapy of 816 days), with the woodchuck hepatitis virus (WHV), human immunodeficiency virus (HIV), and the comparable regions with the DNA polymerase of herpes simplex virus (HSV) (13, 14). The conserved asparagine (D) and glycine (G) residues within the polymerase motifs are in bold type and the amino acid changes found after famciclovir treatment are in bold type and underlined. The location of the mutated amino acid residues within HBV polymerase are shown. The bold face underlined glycine (G) residue in the HSV polymerase becomes a cysteine (C) during penciclovir treatment (15).

[0109]FIG. 4 is a representation showing conserved regions of domain A to E (underlined) of HBV. M in YMDD is designated amino acid number 550. * indicates greater than three amino acid possibilities at this position of the consensus sequence.

[0110]FIG. 5 is a representation showing amino acid alignment of the RNA dependent DNA polymerase sequence motifs from HBV, noting the amino acid changes which have been selected for in the presence of famciclovir and 3TC. HBV concensus sequence was derived from published sequences in Genebank/Entrez. The conserved asparagine (D) and glycine (G) residues within the polymerase motifs are in bold type. The amino acid changes found after famciclovir treatment are in bold green type and underlined and after 3TC are in bold blue type and are underlined. The amino acid sequence of the HBV isolated from patient A and patient B, during famicilovir treatment and from Patient C who did not respond to famciclovir and was later treated with 3TC in which a resistance mutation was selected (3TC 2). The published 3TC changes detected by Ling et al (16) is shown in 3TC 1.

[0111]FIG. 6 is a representation showing the nucleotide sequence of an HBV variant and corresponding amino acid sequences for HBV DNA polymerase and HBV surface antigen showing in bold mutations G498E in the polymerase and D144E and G145R in the surface antigen.

EXAMPLE 1 Case Study

[0112] 1. Patient A

[0113] The inventors sequenced the HBV polymerase and X open reading frames from a series of isolates from a patient who received antiviral therapy for almost 4 years following post liver transplant recurrence of HBV infection (FIG. 2).

[0114] The patient (male, aged 42 years) was transplanted because of end-stage liver failure due to chronic HBV infection. The initial post transplant course was unremarkable but by 5 months there was evidence of recurrent infection and very high levels of viral replication and deteriorating liver function (12). The histological picture was consistent with fibrosing cholestatic hepatitis. Antiviral treatment was commenced approximately 6 months post-OLT. Initially, the patient received intravenous (iv) ganciclovir (GCV; 10 mg/kg/day) in combination with iv foscarnet (PFF; 50-125 mg/kg/day; the dose depending on renal function) (12). This is the treatment of GCV+PFF described in FIG. 1 which lasted for 86 days. Maintenance iv GCV (3.3-6.7 mg/kg/day) three times per week was commenced on day 87 of antiviral treatment (GCV in FIG. 1). Oral famciclovir (250 mg, twice daily) was commenced on day 446 of therapy (FCV [I] in FIG. 1) which was increased to 500 mg twice daily (FCV [II] in FIG. 1) on day 500. The patient is currently on this treatment regime. The clinical and virological details of this patient preceding famciclovir therapy have been reported (12).

[0115] Serum samples were routinely collected and stored at −70° C. Informed consent was obtained from the patient to use these samples for research purposes. FIG. 2 shows the alanine amino transferase (ALT) and HBV DNA levels over the entire course of antiviral treatment. The 5 samples chosen for additional studies cover a period of almost four years.

[0116] 2. Patient B

[0117] Patient B was retransplanted for pre-core mutant associated HBV-related allograph loss 14 months after the initial liver transplant. Antiviral treatment with GCV (7.5 mg/kg/day) was given for 10 months and then ceased. This was followed by oral famciclovir therapy given (500 mg 3 times/day).

[0118] From patient B the entire HBV polymerase gene was sequenced from a serum HBV sample taken post-transplantation after 850 days FCV therapy. The regions encompassing the catalytic domains of the HBV polymerase were sequenced from a serum sample pretransplant prior to FCV treatment.

[0119] 3. Patient C

[0120] This patient did not respond to famciclovir and was later treated with lamivudine (3TC) (6, 7) in which a resistance mutation was selected.

[0121] 4. Patient D

[0122] This patient is treated with famciclovir in which resistance mutation is selected.

EXAMPLE 2 Viral Markers in Serum

[0123] Hepatitis B surface antigen (HbsAg), hepatitis B e antigen (HbeAg), anti-HBe, hepatitis B core antigen (HbcAg) specific IgG and IgM, hepatitis A specific IgM, hepatitis delta antigen and antibody, and anti-hepatitis C virus antibody were measured using commercially available immunoassays (Abbott Laboratories, North Chicago, Ill.). Only the HBV markers were positive. Hepatitis B viral DNA levels were measured and quantified using a capture hybridisation assay according to the manufacturer's directions (Digene Diagnostics Inc., Beltsville, Md.). This patient was infected with a pre-core HBV mutant pre-OLT (12) and this status did not change post-OLT.

EXAMPLE 3 Sequencing and Cloning of HBV DNA

[0124] 1. Extraction of DNA from sera: Aliquots of 50 μl of sera were mixed with 150 μl TE (10 mmol/Tris-HCl (pH 7.5), 2 mmol/L EDTA), 1% w/v sodium dodecyl sulfate and 1 mg/ml pronase and incubated at 37° C. for 2 hours. DNA was deproteinised by phenol/chloroform, precipitated with isopropanol and dissolved in 25 μl nuclease-free water.

[0125] 2. Amplification of the viral polymerase and X genes by polymerase chain reaction (PCR): Oligonucleotides were synthesised by Bresatec, Adelaide, Australia. For amplification of the polymerase gene, the sense primer was 5′-GGA GTG TGG ATT CGC ACT CC-3′ [SEQ ID NO:1] (nucleotides [nt] −40 to −21) and the antisense primer was 5′-GCT CCA AAT TCT TTA TA-3′ [SEQ ID NO:2] (nt 2831 to 2847). For amplification of the X gene, the sense primer was 5′-CCT TTA CCC CGT TGC CCG GC-3′ [SEQ ID NO:3] (nt 2055 to 2074) and the antisense primer 5′-GCT CCA AAT TCT TTA TA-3′ [SEQ ID NO:4] (nt 2831 to 2847). All nt are numbered from the start of the polymerase gene. Each reaction was carried out using 5 μl of the extracted DNA as template, 1.5 U of Taq polymerase (Perkin Elmer Cetus, Norwalk, Conn.), 1 μmol/L of sense and antisense primers, 200 μmol/L each of deoxynucleoside triphosphates, 50 mmol/L Kcl, 3.5 mmol/L MgCl, 10 mmol/L Tris-Hcl (pH 8.3) and 0.01% w/v gelatin. Amplification was achieved by 40 cycles of denaturation (94° C. for 1 min), annealing (55° C. for 1 min) and extension (72° C. for 1.5 min), followed by a final extension of 7 min (Perkin-Elmer Cetus, Norwalk, Conn.). The PCR product was analysed by gel electrophoresis through 1.5% w/v agarose and visualised by UV irradiation after staining with ethidium bromide.

[0126] 3. Sequencing of the polymerase and X genes of HBV DNA: The specific amplified product was purified using Geneclean II (BIO 101 Inc., La Jolla, Calif.) and directly sequenced using Sequenase version 2.0 (United States Biochemical Corp., Cleveland, Ohio). The PCR primers were used as sequencing primers and internal primers were additionally synthesised to sequence the internal regions of the PCR products. The following internal and sequencing primers were used 5′-GCC GCG TCG CAG AAG ATC TCA AT-3′ [SEQ ID NO:5] (nt 104-126), 5′-GGT TCT ATC CTA ACC TTA CC-3′ [SEQ ED NO:6] (nt 341-360), 5′-GCC TCA TTT TGT GGG TCA CCA TA-3′ [SEQ ID NO:7] (nt 496-518), 5′-TGG GGG TGG AGC CCT CAG GCT-3′ [SEQ ID NO:8] (nt 731-751), 5′-CAC AAC ATT CCA CCA AGC TC-3′ [SEQ ID NO:9] (nt 879-899), 5′-AAA TTC GCA GTC CCC AAC-3′ [SEQ ID NO:10] (nt 1183-1195), 5′-GTT TCC CTC TTC TTG CTG T-3′ [SEQ ID NO:11] (nt 1429-1447), 5′-TTT TCT TTT GTC TTT GGG TAT-3′ [SEQ ID NO:12] (nt 1683-1703) 5′-CCA ACT TAC AAG GCC TTT CTG-3′ [SEQ ID NO:13] (nt 1978-1999), 5′-CAT CGT TTC CAT GGC TGC TAG GC-3′ [SEQ ID NO:14] (nt 2239-2262).

[0127] 4. Cloning of the HBV Polymerase Gene into pUC18:

[0128] Due to the small amount of HBV DNA in the samples, the region encompassing nt 1429 to 1703 from the HBV polymerase gene were amplified by PCR using the primers-5′-GTT TCC CTC TTC TTG CTG T-3′ [SEQ ID NO:15] (nt 1429-1447) and 5′ ATA CCC AAA GAC AAA AGA AAA-3′ [SEQ ID NO-16] (nt 1703-1683), before cloning. The DNA was purified with Geneclean II and ligated using T4 DNA ligase (New England Biolabs, Beverly, Mass.) into a SmaI-digested dephosphorylated pUC18 plasmid (Pharmacia Biotech, NJ). Clones were directly sequence as above.

EXAMPLE 4 DNA Polymerase Assay

[0129] Samples of scrum (100 μl) were applied to a 20% w/v sucrose cushion in TNE (20 mmolVL Tris-HCI pH 7.4, 150 mmol/L NaCl₂ 1 mmol/L EDTA) and centrifuged at 200,000 g for 3 hr at 10° C. using an SW41 rotor in a Beckman Model L8 ultracentrifuge. The pellet was resuspended in 50 mmol/L TRIS-HCl pH 7.5 containing 1.5% v/v Triton-X100, 100 nnol/L Kcl and 0.01% v/v 2-mercaptoethanol and allowed to stand overnight at 4° C. Small aliquots of the suspension were assayed for endogenous HBV DNA polymerase activity essentially as described by Price et al (16). Each assay was performed in a total volume of 30 μl which contained 20 μl of the partly purified HBV and (final concentrations) 30 mmol/L Tris-HCl pH 7.5, 30 mmol/L MgCl₂, 10 μmol/L each dATP, dTTP and dGTP, and 0.01 μM [α-³²P]-dCTP (3,000 Ci/mmnol) (Dupont NEN, Boston, Mass.). To test for penciclovir triphosphate (PCV-TP) sensitivity, paired assays were performed on each sample, with an excess (100 μmmol/L penciclovir-triphosphate included in the reaction mixture in one assay of each pair. After 2 hr at 37° C., reactions were stopped by spotting 20 μl aliquots of each reaction mix onto 25 mm diameter glass fibre discs (Advantex, Tokyo, Japan) which had ben pre-soaked in 10% w/v trichloroacetic acid (TCA). Discs were dried before washing in ice-cold 10% w/v TCA containing 10 mmol/L sodium pyrophosphate.

[0130] Three further 10 min washes in cold 5% v/v TCA followed. The washed discs were finally rinsed in absolute ethanol air dried, and counted for radioactivity. Inhibition of HBV DNA polymerase activity by PCV-TP was expressed as the percentage difference in activity in the assay mix containing PCV-TP compared to the matched control. Because of limited sample amounts, it was not possible to standardize enzyme activity or to perform replicate assays. Despite the inherent variability of the assay, a general time related decrease in sensitivity of the HBV DNA polymerase to PCV-TP was evident (see Table 1).

EXAMPLE 5 Effect of Antiviral Therapy

[0131] Upon commencement of the antiviral treatment strategy GCV+PFF, the level of HBV DNA post-OLT decreased from over 100,000 pg/ml to 10,800 pg/ml by day 87 (FIG. 1). This reduction in viraemnia was associated with clinical, biochemical and histological improvement (12). Maintenance famciclovir therapy (treatment GCV) resulted in fluctuating levels of HBV DNA over the ensuring 359 days with two peaks of HBV DNA observed. The switch to oral famciclovir on day 446 was also associated with a rise in HBV DNA, but this was likely to have been the result of insufficient dosing (FCV[I] in FIG. 2) rather than a breakthrough in treatment. Following dose increase to FCV [II] on day 500, there was a decrease in HBV DNA. However, the level of HBV DNA gradually rose over time from 3,000 pg/ml on day 600 (154 days of famciclovir), to 8,800 pg/ml on day 816 (370 days famciclovir), peaking at 29,000 pg/ml on day 1302 (856 days of famciclovir), then stabilising at around 12,000 pg/ml on day 1329 (883 days of famciclovir). A students test of the DNA levels during the treatment period from days 816 to days 1329, revealed statistically significant rise. There was a 1.5 to 2 fold rise in ALT levels over the same time interval (FIG. 2) and no change in clinical status.

EXAMPLE 6 Nucleotide Changes

[0132] The X and the polymerase genes of HBV were sequenced at five time points (FIG. 2). During almost 4 years of the antiviral therapy there were no changes in the X gene compared to the pretreatment sequence. However, there were 5 nt changes detected in the polymerase gene from day 816 and day 1329 samples (Table 1). These changes were detected in separate independent PCR amplifications; furthermore the mutations were detected by sequencing both strands and are therefore unlikely to be the result of PCR generated errors. The nt changes in the polymerase gene were first detected after 816 days of treatment, when the patient had been treated with famciclovir for 370 days. However, only two nt changes, at positions 1498 and 1519 resulted in amino acid changes, Val 519-Leu and Leu 526-Met, respectively. These two nt changes appeared concurrently. At 816 days, three different nt (C,G,T) were detected at position 1498 (all of which would result in a Val to Leu change). After 1329 days post-treatment, thymidine was the dominant species at nt 1498. The amino acid changes at 816 and 1329 days post treatment coincided with reduced serum HBV DNA polymerase sensitivity to PCV-TP (Table 1). These nt changes were not found in 6 patients with post-OLT recurrent HBV infection who were not undergoing FCV therapy.

[0133] The region encompassing the nt mutations which gave rise to amino acid changes from the sample taken at 1329 days was cloned and sequenced. Three quasi-species were detected. Seventy-five percent (15/20) of the clones contained both the 1498 and 1519 mutations which occurred together. Pretreatment non-mutated sequences were detected in 3/20 of the clones. A further mutation at nt 1511, which would result in a proline to leucine change at position 523, was detected in 2/20 of the clones. This mutation was not detected with the two dominant mutations, 1498 (Val 519-Leu) and 1519 (Lcu 526-Met), nor was it detected by direct PCR sequencing, indicating it probably occurs at a low frequency. Viral DNA from the sample obtained at 600 days (150 days of FCV treatment) was also cloned and sequenced; however, only the pre-treatment sequences were detected.

EXAMPLE 7 Nucleotide Changes in Patients B, C and D

[0134] The amino acid changes in HBV isolated from patients B and C are shown in FIG. 5, and from patient D is shown in FIG. 6. In FIG. 5, patient A is the same as shown in FIG. 3.

[0135] Patient B was undergoing long term famciclovir treatment (>850 days). The amino acid change selected during famciclovir treatment is shown as HBV (patient B) in FIG. 5. Patient C did not respond to famciclovir and was later treated with 3TC (lamivudine [6,7]). The HBV isolated during FCV treatment from patient C, is shown as HBV (patient C-FCV). All 3TC resistance mutations which developed during treatment with 3TC is shown as HBV (patient C-3TC). The sequence analysis showed a mutation (Thr-Ser substitution) in the HBV polymerase gene near the C domain but no mutation was initially detected in the YMDD motif. A mutation of Met 550 to Ile in the YMDD motif was detected from HBV isolated 32 days (333 days post treatment) after the HBV containing the Thr-Ser substitution was isolated.

EXAMPLE 8 Escape Mutants

[0136] Using the method hereinbefore described, HBV variants are screened for escape mutations. These are mutations in surface components such as the HBV surface antigen which reduce the interactivity of the surface component to antibodies or other immunological reagents. Given the overlapping open reading frame of HBV genome, a single mutation may have multiphenotypic consequences. For example, a mutation in the HBV DNA polymerase may also have an affect on the HBV surface antigen.

[0137] Preferred mutations in the HBV surface antigen are in amino acids 118 to 169 and/or 169 to 207 such as D144E or G145R. These correspond to DNA polymerase mutations G498E and V499L.

[0138] A particularly preferred escape mutant and nucleoside analogue resistant mutant has a nucleotide sequence set forth in FIG. 6 with corresponding amino acid sequences for the DNA polymerase and surface antigen.

[0139] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications. The invention also includes all of the steps, features, compositions and compounds referred to or indicated in is specification, individually or collectively, and any and all combinations of any two or more of said steps or features. TABLE 1 Nucleotide mutations in the polymerase gene and the resulting amino acid changes during antiviral therapy Inhibition of Days of Days post HBV DNA antiviral famciclovir POLYMERASE GENE Polymerase by treatment treatment nt 297 nt 1498 nt 1511* nt 1519 nt 2008 nt 2331 PCV-TP** Pretreatment NR*** T G C C C G 40%  87 NR — — — — — — NA****  600 154 — — — — — — 30%  816 370 — G, T, C — A — —  0% 1329 883 C T T A A A  0% Amino acid change None Val 519- Pro 523- Leu 526- None None Leu Leu Met

BIBLIOGRAPHY

[0140] 1. Summers J, Mason W. Cell (1982) 29: 403-415.

[0141] 2. Vere Hodge R. A. Antiviral Chem Chemother (1993) 4:67-84.

[0142] 3. Boyd M R et al Antiviral Chem Chemother. (1987) 32: 358-363.

[0143] 4. Kruger T et al Hepatology (1994) 22: 219A.

[0144] 5. Main J et al. J. Viral Hepatitis (1996) 3:211-215.

[0145] 6. Severini A et al Antimicrobial Agents Chemother (1995) 39: 1430-1435.

[0146] 7. Dienstag J L et al New England J Med (1995) 333: 1657-1661.

[0147] 8. Shaw T, et al. Antimicrobiol Agents Chemother (1994) 38:719-723.

[0148] 9. Shaw T, et al. Hepatology (1996) 24: in press.

[0149] 10. Tsiquaye K N, et al. J. Med Virol (1994) 42: 306-310.

[0150] 11. Boker K H W, et al. Transplantation (1994) 57: 1706-1708.

[0151] 12. Angus P, et al. J. Gastroenterol Hepatol (1993) 8: 353-357.

[0152] 13. Poch O, et al. EMBO J. (1989) 8: 3867-3874.

[0153] 14. Delarue M, et al. Protein Engineering (1990) 3: 461-467.

[0154] 15. Chiou H C, et al. Antiviral Chem Chemother (1995) 6: 281-288.

[0155] 16. Ling R, et al. Hepatology (1996) 24: 711-713.

[0156] 17. Price P M, et al. Hepatology 1992 16: 8-13.

1 57 1 20 DNA Hepatitis B virus 1 ggagtgtgga ttcgcactcc 20 2 17 DNA Hepatitis B virus 2 gctccaaatt ctttata 17 3 20 DNA Hepatitis B virus 3 cctttacccc gttgcccggc 20 4 17 DNA Hepatitis B virus 4 gctccaaatt ctttata 17 5 23 DNA Hepatitis B virus 5 gccgcgtcgc agaagatctc aat 23 6 20 DNA Hepatitis B virus 6 ggttctatcc taaccttacc 20 7 23 DNA Hepatitis B virus 7 gcctcatttt gtgggtcacc ata 23 8 21 DNA Hepatitis B virus 8 tgggggtgga gccctcaggc t 21 9 20 DNA Hepatitis B virus 9 cacaacattc caccaagctc 20 10 18 DNA Hepatitis B virus 10 aaattcgcag tccccaac 18 11 19 DNA Hepatitis B virus 11 gtttccctct tcttgctgt 19 12 21 DNA Hepatitis B virus 12 ttttcttttg tctttgggta t 21 13 21 DNA Hepatitis B virus 13 ccaacttaca aggcctttct g 21 14 23 DNA Hepatitis B virus 14 catcgtttcc atggctgcta ggc 23 15 19 DNA Hepatitis B virus 15 gtttccctct tcttgctgt 19 16 21 DNA Hepatitis B virus 16 atacccaaag acaaaagaaa a 21 17 550 DNA Hepatitis B virus CDS (1)..(549) 17 tct tcc aat ttg tcc tgg tta tcg ctg gat gtg tct gcg gcg ttt tat 48 Ser Ser Asn Leu Ser Trp Leu Ser Leu Asp Val Ser Ala Ala Phe Tyr 1 5 10 15 cat att cct ctt cat cct gct gct atg cct cat ctt ctt att ggt tct 96 His Ile Pro Leu His Pro Ala Ala Met Pro His Leu Leu Ile Gly Ser 20 25 30 tct gga tta tca agg tat gtt gcc cgt ttg tcc tct aat tcc agg atc 144 Ser Gly Leu Ser Arg Tyr Val Ala Arg Leu Ser Ser Asn Ser Arg Ile 35 40 45 aac aac aac atg caa aac ctg cac gac tcc tgc tca agg caa ctc tac 192 Asn Asn Asn Met Gln Asn Leu His Asp Ser Cys Ser Arg Gln Leu Tyr 50 55 60 gtt tcc ctc atg ttg ctg tac aaa acc tac gga gag aaa ttg cac ctg 240 Val Ser Leu Met Leu Leu Tyr Lys Thr Tyr Gly Glu Lys Leu His Leu 65 70 75 80 tat tcc cat ccc atc gtc ctg ggc ttt cgc aaa ata cct atg gga gtg 288 Tyr Ser His Pro Ile Val Leu Gly Phe Arg Lys Ile Pro Met Gly Val 85 90 95 ggc ctc agt ccg ttt ctc ttg gct cag ttt act agt gcc att tgt tca 336 Gly Leu Ser Pro Phe Leu Leu Ala Gln Phe Thr Ser Ala Ile Cys Ser 100 105 110 gtg gtt cgt agg gct ttc ccc cac tgt ttg gct ttc agc tat atg gat 384 Val Val Arg Arg Ala Phe Pro His Cys Leu Ala Phe Ser Tyr Met Asp 115 120 125 gat gtg gta ttg ggg gcc aag tct gta cag cat cgt gag gcc ctt tat 432 Asp Val Val Leu Gly Ala Lys Ser Val Gln His Arg Glu Ala Leu Tyr 130 135 140 acc gct gtt acc aat ttt ctt ttg tct ctg ggt ata cat tta aac cct 480 Thr Ala Val Thr Asn Phe Leu Leu Ser Leu Gly Ile His Leu Asn Pro 145 150 155 160 aac aaa aca aaa aga tgg ggt tat tcc cta aac ttc atg ggt tac ata 528 Asn Lys Thr Lys Arg Trp Gly Tyr Ser Leu Asn Phe Met Gly Tyr Ile 165 170 175 att gga agt tgg gga aca ttg c 550 Ile Gly Ser Trp Gly Thr Leu 180 18 183 PRT Hepatitis B virus 18 Ser Ser Asn Leu Ser Trp Leu Ser Leu Asp Val Ser Ala Ala Phe Tyr 1 5 10 15 His Ile Pro Leu His Pro Ala Ala Met Pro His Leu Leu Ile Gly Ser 20 25 30 Ser Gly Leu Ser Arg Tyr Val Ala Arg Leu Ser Ser Asn Ser Arg Ile 35 40 45 Asn Asn Asn Met Gln Asn Leu His Asp Ser Cys Ser Arg Gln Leu Tyr 50 55 60 Val Ser Leu Met Leu Leu Tyr Lys Thr Tyr Gly Glu Lys Leu His Leu 65 70 75 80 Tyr Ser His Pro Ile Val Leu Gly Phe Arg Lys Ile Pro Met Gly Val 85 90 95 Gly Leu Ser Pro Phe Leu Leu Ala Gln Phe Thr Ser Ala Ile Cys Ser 100 105 110 Val Val Arg Arg Ala Phe Pro His Cys Leu Ala Phe Ser Tyr Met Asp 115 120 125 Asp Val Val Leu Gly Ala Lys Ser Val Gln His Arg Glu Ala Leu Tyr 130 135 140 Thr Ala Val Thr Asn Phe Leu Leu Ser Leu Gly Ile His Leu Asn Pro 145 150 155 160 Asn Lys Thr Lys Arg Trp Gly Tyr Ser Leu Asn Phe Met Gly Tyr Ile 165 170 175 Ile Gly Ser Trp Gly Thr Leu 180 19 550 DNA Hepatitis B virus CDS (2)..(472) CDS (476)..(508) CDS (512)..(526) CDS (530)..(550) 19 t ctt cca att tgt cct ggt tat cgc tgg atg tgt ctg cgg cgt ttt atc 49 Leu Pro Ile Cys Pro Gly Tyr Arg Trp Met Cys Leu Arg Arg Phe Ile 1 5 10 15 ata ttc ctc ttc atc ctg ctg cta tgc ctc atc ttc tta ttg gtt ctt 97 Ile Phe Leu Phe Ile Leu Leu Leu Cys Leu Ile Phe Leu Leu Val Leu 20 25 30 ctg gat tat caa ggt atg ttg ccc gtt tgt cct cta att cca gga tca 145 Leu Asp Tyr Gln Gly Met Leu Pro Val Cys Pro Leu Ile Pro Gly Ser 35 40 45 aca aca aca tgc aaa acc tgc acg act cct gct caa ggc aac tct acg 193 Thr Thr Thr Cys Lys Thr Cys Thr Thr Pro Ala Gln Gly Asn Ser Thr 50 55 60 ttt ccc tca tgt tgc tgt aca aaa cct acg gag aga aat tgc acc tgt 241 Phe Pro Ser Cys Cys Cys Thr Lys Pro Thr Glu Arg Asn Cys Thr Cys 65 70 75 80 att ccc atc cca tcg tcc tgg gct ttc gca aaa tac cta tgg gag tgg 289 Ile Pro Ile Pro Ser Ser Trp Ala Phe Ala Lys Tyr Leu Trp Glu Trp 85 90 95 gcc tca gtc cgt ttc tct tgg ctc agt tta cta gtg cca ttt gtt cag 337 Ala Ser Val Arg Phe Ser Trp Leu Ser Leu Leu Val Pro Phe Val Gln 100 105 110 tgg ttc gta ggg ctt tcc ccc act gtt tgg ctt tca gct ata tgg atg 385 Trp Phe Val Gly Leu Ser Pro Thr Val Trp Leu Ser Ala Ile Trp Met 115 120 125 atg tgg tat tgg ggg cca agt ctg tac agc atc gtg agg ccc ttt ata 433 Met Trp Tyr Trp Gly Pro Ser Leu Tyr Ser Ile Val Arg Pro Phe Ile 130 135 140 ccg ctg tta cca att ttc ttt tgt ctc tgg gta tac att taa acc cta 481 Pro Leu Leu Pro Ile Phe Phe Cys Leu Trp Val Tyr Ile Thr Leu 145 150 155 aca aaa caa aaa gat ggg gtt att ccc taa act tca tgg gtt aca taa 529 Thr Lys Gln Lys Asp Gly Val Ile Pro Thr Ser Trp Val Thr 160 165 170 ttg gaa gtt ggg gaa cat tgc 550 Leu Glu Val Gly Glu His Cys 175 180 20 157 PRT Hepatitis B virus 20 Leu Pro Ile Cys Pro Gly Tyr Arg Trp Met Cys Leu Arg Arg Phe Ile 1 5 10 15 Ile Phe Leu Phe Ile Leu Leu Leu Cys Leu Ile Phe Leu Leu Val Leu 20 25 30 Leu Asp Tyr Gln Gly Met Leu Pro Val Cys Pro Leu Ile Pro Gly Ser 35 40 45 Thr Thr Thr Cys Lys Thr Cys Thr Thr Pro Ala Gln Gly Asn Ser Thr 50 55 60 Phe Pro Ser Cys Cys Cys Thr Lys Pro Thr Glu Arg Asn Cys Thr Cys 65 70 75 80 Ile Pro Ile Pro Ser Ser Trp Ala Phe Ala Lys Tyr Leu Trp Glu Trp 85 90 95 Ala Ser Val Arg Phe Ser Trp Leu Ser Leu Leu Val Pro Phe Val Gln 100 105 110 Trp Phe Val Gly Leu Ser Pro Thr Val Trp Leu Ser Ala Ile Trp Met 115 120 125 Met Trp Tyr Trp Gly Pro Ser Leu Tyr Ser Ile Val Arg Pro Phe Ile 130 135 140 Pro Leu Leu Pro Ile Phe Phe Cys Leu Trp Val Tyr Ile 145 150 155 21 11 PRT Hepatitis B virus 21 Thr Leu Thr Lys Gln Lys Asp Gly Val Ile Pro 1 5 10 22 5 PRT Hepatitis B virus 22 Thr Ser Trp Val Thr 1 5 23 7 PRT Hepatitis B virus 23 Leu Glu Val Gly Glu His Cys 1 5 24 25 PRT Hepatitis B virus VARIANT (1) Xaa = Ser or Ala 24 Xaa His Pro Ile Xaa Leu Gly Phe Arg Lys Xaa Pro Met Gly Xaa Gly 1 5 10 15 Leu Ser Pro Phe Leu Leu Ala Gln Phe 20 25 25 41 PRT Hepatitis B virus VARIANT (1) Xaa = Gln or Lys 25 Xaa Thr Xaa Gly Xaa Lys Leu His Leu Xaa Xaa His Pro Ile Xaa Leu 1 5 10 15 Gly Phe Arg Lys Xaa Pro Met Gly Xaa Gly Leu Ser Pro Phe Leu Leu 20 25 30 Ala Gln Phe Thr Ser Ala Ile Xaa Ser 35 40 26 11 PRT Hepatitis B virus VARIANT (1) Xaa = Ala or Val 26 Xaa Phe Xaa Tyr Met Asp Asp Xaa Val Leu Gly 1 5 10 27 30 PRT Hepatitis B virus VARIANT (1) Xaa = Ser or Ala 27 Xaa His Pro Ile Xaa Leu Gly Xaa Arg Lys Xaa Pro Met Gly Xaa Gly 1 5 10 15 Leu Ser Xaa Phe Leu Xaa Ala Gln Phe Thr Ser Ala Xaa Xaa 20 25 30 28 14 PRT Hepatitis B virus VARIANT (1) Xaa = Ala or Val 28 Xaa Phe Xaa Tyr Xaa Asp Asp Xaa Val Leu Gly Ala Xaa Xaa 1 5 10 29 181 PRT Hepatitis B virus VARIANT (2) Xaa = Asn or Asp 29 Ser Xaa Leu Ser Trp Leu Ser Leu Asp Val Ser Ala Ala Phe Tyr His 1 5 10 15 Xaa Pro Leu His Pro Ala Ala Met Pro His Leu Leu Xaa Gly Ser Ser 20 25 30 Gly Leu Xaa Arg Tyr Val Ala Arg Leu Ser Ser Xaa Ser Xaa Xaa Xaa 35 40 45 Asn Xaa Gln Xaa Xaa Xaa Xaa Xaa Xaa Leu His Xaa Xaa Cys Ser Arg 50 55 60 Xaa Leu Tyr Val Ser Leu Xaa Leu Leu Tyr Xaa Thr Xaa Gly Xaa Lys 65 70 75 80 Leu His Leu Xaa Xaa His Pro Ile Xaa Leu Gly Phe Arg Lys Xaa Pro 85 90 95 Met Gly Xaa Gly Leu Ser Pro Phe Leu Leu Ala Gln Phe Thr Ser Ala 100 105 110 Ile Xaa Xaa Xaa Xaa Xaa Arg Ala Phe Xaa His Cys Xaa Xaa Phe Xaa 115 120 125 Tyr Met Asp Asp Xaa Val Leu Gly Ala Xaa Xaa Xaa Xaa His Xaa Glu 130 135 140 Xaa Leu Xaa Xaa Xaa Xaa Xaa Xaa Xaa Leu Leu Xaa Xaa Gly Ile His 145 150 155 160 Leu Asn Pro Xaa Lys Thr Lys Arg Trp Gly Tyr Ser Leu Asn Phe Met 165 170 175 Gly Tyr Xaa Ile Gly 180 30 4 PRT Hepatitis B virus 30 Tyr Met Asp Asp 1 31 11 PRT Hepatitis B virus 31 Ala Phe Ser Tyr Met Asp Asp Val Val Leu Gly 1 5 10 32 11 PRT Hepatitis B virus 32 Ala Phe Ser Tyr Met Asp Asp Val Val Leu Gly 1 5 10 33 11 PRT Hepatitis B virus 33 Val Phe Ala Tyr Met Asp Asp Leu Val Leu Gly 1 5 10 34 11 PRT Hepatitis B virus 34 Ile Tyr Gln Tyr Met Asp Asp Leu Tyr Val Gly 1 5 10 35 33 PRT Hepatitis B virus 35 Thr Thr Ile Gly Arg Glu Met Leu Leu Ala Thr Arg Glu Tyr Val His 1 5 10 15 Ala Arg Trp Ala Ala Phe Glu Gln Leu Leu Ala Asp Phe Pro Glu Ala 20 25 30 Ala 36 41 PRT Hepatitis B virus 36 Gln Thr Phe Gly Arg Lys Leu His Leu Tyr Ser His Pro Ile Ile Leu 1 5 10 15 Gly Phe Arg Lys Ile Pro Met Gly Leu Gly Leu Ser Leu Phe Leu Met 20 25 30 Ala Gln Phe Thr Ser Ala Ile Cys Ser 35 40 37 41 PRT Hepatitis B virus 37 Gln Thr Phe Gly Arg Lys Leu His Leu Tyr Ser His Pro Ile Ile Leu 1 5 10 15 Gly Phe Arg Lys Ile Pro Met Gly Val Gly Leu Ser Pro Phe Leu Met 20 25 30 Ala Gln Phe Thr Ser Ala Ile Cys Ser 35 40 38 41 PRT Hepatitis B virus 38 Gln Thr Phe Gly Arg Lys Leu His Leu Tyr Ser His Pro Ile Ile Leu 1 5 10 15 Gly Leu Arg Lys Ile Pro Met Gly Val Gly Leu Ser Pro Phe Leu Met 20 25 30 Ala Gln Phe Thr Ser Ala Ile Cys Ser 35 40 39 41 PRT Hepatitis B virus 39 Gln Thr Phe Gly Arg Lys Leu His Leu Tyr Ser His Pro Ile Val Leu 1 5 10 15 Gly Phe Arg Lys Ile Pro Met Gly Val Gly Leu Ser Pro Phe Leu Leu 20 25 30 Ala Gln Phe Thr Ser Ala Leu Cys Ser 35 40 40 14 PRT Hepatitis B virus 40 Ala Phe Ser Tyr Met Asp Asp Val Val Leu Gly Ala Lys Thr 1 5 10 41 31 PRT Hepatitis B virus VARIANT (1) Xaa = Ser or Ala 41 Xaa His Pro Ile Xaa Leu Gly Phe Arg Lys Xaa Pro Met Gly Xaa Gly 1 5 10 15 Leu Ser Pro Phe Leu Leu Ala Gln Phe Thr Ser Ala Ile Cys Ser 20 25 30 42 40 PRT Hepatitis B virus VARIANT (1) Xaa = Gln or Lys 42 Xaa Thr Xaa Gly Xaa Lys Leu His Leu Xaa Xaa His Pro Ile Xaa Leu 1 5 10 15 Gly Xaa Arg Lys Xaa Pro Met Gly Xaa Gly Leu Ser Xaa Phe Leu Xaa 20 25 30 Ala Gln Phe Thr Ser Ala Xaa Xaa 35 40 43 14 PRT Hepatitis B virus VARIANT (1) Xaa = Ala or Val 43 Xaa Phe Xaa Tyr Xaa Asp Asp Xaa Val Leu Gly Ala Xaa Xaa 1 5 10 44 31 PRT Hepatitis B virus VARIANT (1) Xaa = Ser or Ala 44 Xaa His Pro Ile Xaa Leu Gly Phe Arg Lys Xaa Pro Met Gly Xaa Gly 1 5 10 15 Leu Ser Pro Phe Leu Leu Ala Gln Phe Thr Ser Ala Ile Xaa Ser 20 25 30 45 14 PRT Hepatitis B virus VARIANT (1) Xaa = Ala or Val 45 Xaa Phe Xaa Tyr Met Asp Asp Xaa Val Leu Gly Ala Xaa Xaa 1 5 10 46 11 PRT Hepatitis B virus 46 Ala Phe Ser Tyr Met Asp Asp Val Val Leu Gly 1 5 10 47 11 PRT Hepatitis B virus 47 Ala Phe Ser Tyr Met Asp Asp Val Val Leu Gly 1 5 10 48 11 PRT Hepatitis B virus VARIANT (5) Xaa = Val or Ile 48 Ala Phe Ser Tyr Xaa Asp Asp Val Val Leu Gly 1 5 10 49 11 PRT Hepatitis B virus 49 Ala Phe Ser Tyr Met Asp Asp Val Val Leu Gly 1 5 10 50 16 PRT Hepatitis B virus 50 Ser Asp Leu Ser Trp Leu Ser Leu Asp Val Ser Ala Ala Phe Tyr His 1 5 10 15 51 16 PRT Hepatitis B virus 51 Ser Asp Leu Ser Trp Leu Ser Leu Asp Val Ser Ala Ala Phe Tyr His 1 5 10 15 52 16 PRT Hepatitis B virus 52 Thr Asp Leu Gln Trp Leu Ser Leu Asp Val Ser Ala Ala Phe Tyr His 1 5 10 15 53 16 PRT Hepatitis B virus 53 Lys Lys Lys Ser Val Thr Val Leu Asp Val Gly Asp Ala Tyr Phe Ser 1 5 10 15 54 41 PRT Hepatitis B virus 54 Gln Thr Phe Gly Arg Lys Leu His Leu Tyr Ser His Pro Ile Ile Leu 1 5 10 15 Gly Phe Arg Lys Ile Pro Met Gly Val Gly Leu Ser Pro Phe Leu Leu 20 25 30 Ala Gln Phe Thr Ser Ala Ile Cys Ser 35 40 55 41 PRT Hepatitis B virus 55 Gln Thr Phe Gly Arg Lys Leu His Leu Tyr Ser His Pro Ile Ile Leu 1 5 10 15 Gly Phe Arg Lys Ile Pro Met Gly Leu Gly Leu Ser Leu Phe Leu Met 20 25 30 Ala Gln Phe Thr Ser Ala Ile Cys Ser 35 40 56 41 PRT Hepatitis B virus 56 Lys Thr Tyr Gly Arg Lys Leu His Leu Leu Ala His Pro Phe Ile Met 1 5 10 15 Gly Phe Arg Lys Leu Phe Met Gly Val Gly Leu Ser Pro Phe Leu Leu 20 25 30 Ala Gln Phe Thr Ser Ala Leu Ala Ser 35 40 57 27 PRT Hepatitis B virus 57 Arg Tyr Gln Tyr Asn Val Leu Pro Gln Gly Trp Lys Gly Ser Pro Ala 1 5 10 15 Ile Phe Gln Ser Ser Met Thr Lys Ile Leu Glu 20 25 

1. A variant of an isolated DNA virus which replicates via an RNA intermediate wherein said variant comprises a nucleotide mutation in a gene encoding a DNA polymerase or part thereof resulting in at least one amino acid addition, substitution and/or deletion to said DNA polymerase.
 2. A variant of an isolated DNA virus which replicates via a RNA intermediate wherein said variant comprises a nucleotide mutation in a gene encoding a surface component or a part thereof resulting in at least one amino acid addition, substitution and/or deletion to said surface component.
 3. A variant of an isolated DNA virus which replicates via an RNA intermediate at least wherein said variant comprises a nucleotide mutation in an overlapping portion of at least two open reading frames resulting in an amino acid addition, substitution and/or deletion to translation products of said two open reading frames.
 4. A variant according to claim 1 or 2 or 3 wherein said DNA virus is hepatitis B virus (HBV).
 5. A variant according to claim 1 or 3 wherein the amino acid mutation is in the B domain and/or C domain of the HBV DNA polymerase.
 6. A variant according to claim 2 or 3 wherein the amino acid mutation corresponds to the B domain and/or C domain of the HBV DNA polymerase.
 7. A variant according to claim 1 or 3 comprising a mutation in one or more of amino acids within the sequence: Q/K T Y/F G R/W KLHL Y/L S/A HPI IV LGFRK I/L PMG V/G GLS PFLL AQFTSAI C/L S of HBV DNA polymerase.
 8. A variant according to claim 7 comprising a mutation in one or more amino acids within the sequence: S/A HPI I/V LGFRK I/L PMG V/G GLSPFLLAQFTSAIC/L S of HBV DNA polymerase.
 9. A variant according to claim 1 or 3 comprising a nucleotide sequence which encodes a DNA polymerase having the amino acid sequence: X₁HPIX₂LGX₃RKX₄PMGX₅GLSX₆FLX₇AQFTSAX₈X₉ . . . X₁₀FX₁₁YX₁₂DDX₁₃VLGAX₁₄X₁₅ wherein X₁ is S or A; X₂ is I or V; X₃ is F or L; X₄is I or L; X₅ is L or V or G; X₆ is P or L; X₇ is L or M; X₈ is I or L; X₉ is C or L; X₁₀ is A or V; X₁₁ is S or A; X₁₂ is M or I or V; X₁₃is V or L or M; X₁₄ is K or R; and/or X₁₅ S or T; and wherein said variant exhibits reduced sensitivity to a nucleoside sensitivity to a nucleoside analogue, such as famciclovir (penciclovir) and/or lamivudine (3TC).
 10. A variant according to claim 2 or 3 having a mutation in one or more of amino acids 118 to 169 or 169 to 207 of HBV surface antigen.
 11. A variant according to claim 10 comprising a DNA polymerase having the amino acid sequence: X₁₆TX₁₇X₁₈X₁₉KLHLX₂₀X₂₁HPX₂₂LGX₃RKX₄PMGX₅GLSX₆FLX₇AQFTSAX₈X₉ . . . X₁₀FX₁₁YM₁₂DDX₁₃VLGAX₁₄X₁₅ wherein: X₁₆ is Q or K; X₁₇ is Y or F; X₁₈ is G or E; X₁₉ is R or W or K; X₂₀ is Y or L; X₂₁ is S or A; X₂₂ is I or V; X₃ is F or L; X₄ is I or L; X₅ is L or V or G; X₆ is P or L; X₇ is L or M; X₈ is I or L; X₉ is C or L; X₁₀ is A or V; X₁₁ is S or A; X₁₂ is M or I or V; X₁₃ is V or L or M; X₁₄ is K or R; and/or X₁₅ S or T; and wherein said variant exhibits reduced sensitivity to a nucleoside sensitivity to a nucleoside analogue, such as famciclovir (penciclovir) and/or lamivudine (3TC).
 12. A variant according to claim 1 or 2 or 3 selected from Ile509Val, Phe512Leu, Val519Leu, Pro523Leu, Leu526Met, Ile533Leu, Met550Val/Ile, Ser559Thr, Gly498Glu, Arg/Trp499Lys, Thr530Ser.
 13. An HBV variant comprising a mutation in the nucleotide sequence encoding a DNA polymerase resulting in an amino acid addition, substitution and/or deletion in said DNA polymerase in its B domain and/or C domain or in a region proximal thereto, provided said mutation is not in the YMDD motif of the C domain alone, and wherein said variant exhibits decreased sensitivity to a nucleoside analogue.
 14. An HBV variant comprising a mutation in the nucleotide sequence encoding a viral surface component resulting in an amino acid addition, substitution and/or deletion in said viral surface component in a region corresponding to the B domain and/or C domain of HBV DNA polymerase or a region proximal to the B domain and/or C domain of HBV DNA polymerase and wherein said variant exhibits decreased interactivity of immunological reagents to said viral surface component.
 15. An HBV variant comprising a mutation in the nucleotide sequence encoding a viral surface component resulting in an amino acid addition, substitution and/or addition in said viral surface component in a region defined by amino acids 118 to 169 and/or 169 to 207 of the HBV surface antigen or functionally equivalent region wherein said variant exhibits decreased interactivity of immunological reagents to said viral surface component.
 16. An HBV variant comprising a mutation in an overlapping open reading frame in its genome wherein said mutation is in the B and/or C domain of DNA polymerase provided that it is not in the YMDD motif of the C domain alone; and in the overlapping region corresponding to amino acids 118 to 169 and/or 169 to 207 or equivalent of HBV surface antigen and wherein said variant exhibits decreased sensitivity to a nucleotide analogue and exhibits decreased interactivity to immunological reagents specific to HBV surface antigens.
 17. Accordingly, the present invention is directed to an HBV having the nucleotide sequence as set forth in SEQ ID NO:17 or a derivative thereof having a single or multiple nucleotide addition, substitution and/or deletion thereto such as a nucleotide sequence having at least 60% similarity to SEQ ID NO:17.
 18. A variant HBV exhibiting reduced sensitivity to a nucleoside analogue and reduced interactivity to an antibody to wild-type HBV surface antigen, said HBV variant characterised by one or more of the following characteristics: (i) a nucleotide sequence of its genome as set forth in SEQ ID NO:17 or a sequence having at least 60% similarity thereto; (ii) a nucleotide sequence capable of hybridising to SEQ ID NO:17 under low stringency conditions at 42° C.; (iii) a mutation in an overlapping portion of open reading frames for DNA polymerization and HBV surface antigen; and (iv) a mutation in the B and/or C domain of HBV DNA polymerase and is a region corresponding to amino acids 118 to 169 and/or 169 to 207 of HBV surface antigen.
 19. A method for a method for determining the potential for an HBV to exhibit reduced sensitivity to a nuclcoside analogue, said method comprising isolating DNA or corresponding mRNA from said HBV and screening for a mutation in the nucleotide sequence encoding HBV DNA polymerase resulting in at least one amino acid substitution, deletion and/or addition in the B domain or C domain or a region proximal thereto of said DNA polymerase wherein the presence of such a mutation is an indication of the likelihood of resistance to said nucleoside analogue.
 20. A method for determining the potential for an HBV to exhibit reduced interactivity to antibody to HBV surface antigen, said method comprising isolating DNA or corresponding mRNA from said HBV and screening for a mutation in the nucleotide sequence encoding HBV surface antigen resulting in at least one amino acid substitution, deletion and/or addition in amino acids 18 to 169 and/or 169 to 207 of said surface antigen or a region proximal thereto of said surface antigen wherein the presence of such a mutation is an indication of the likelihood of reducing interactivity of said antibodies to said mutated surface antigen.
 21. A method according to claim 19 or 20 wherein the assay detects a mutation selected from Ile509Val, Phe512Leu, Val519Leu, Pro523Leu, Leu526met, Ile533Leu, Met550Val/Ile, Ser559Thr, Gly498Glu, Arg/Trp499Lys, Thr530Ser.
 22. A method for determining whether an HBV isolate encodes a variant DNA polymerase, said method comprising determining the amino acid sequence of its DNA polymerase directly or via a nucleotide sequence and comparing same to the amino acid sequence below:          DOMAIN A 421        430         440         450 S^(N) _(D)LSWLSLD VSAAFYH ^(I) _(P)PL HPAAMPHLL^(I) _(V) GSSGL^(S) _(D)RYVA 460           470             480           490 RLSS^(T) _(N)S^(R) _(N) ^(N) _(I)*N ^(N)Y_(H)Q^(H) _(Y) ^(G) _(R)***^(D) _(N)LH ^(D) _(N) ^(S) _(Y)CSR^(N) _(Q)LYVS L^(L) _(M)LLY^(K) _(Q)T^(Y) _(F)G^(R) _(W)                 DOMAIN B 500           510          520         530 KLHL^(Y)L ^(S)AHPI^(I)V LGFRK^(I)LPMG^(V) _(G) GLSPFLLAQF TSAI^(C) _(L) ^(A) _(S) ^(V) _(M) ^(V) _(T) ^(R) _(C)R                 DOMAIN C 540             550             560 AF^(F) _(P)HC^(L) _(V ^(A) VF^(S) AY MDD^(V)LMVLGA) ^(K) _(R) ^(S) _(T) ^(V) _(G)Q_(E)H^(L)S_(R)E^(S) _(F)L^(F) _(Y) ^(T) _(A) ^(A) _(S)                 DOMAIN D         DOMAIN E 570              580         590          600 ^(V) _(I) ^(T)C^(N)S^(F) _(V)LL ^(S) _(D) ^(L) _(V)GI HLNP^(N) _(Q)KTKRW GYSLNFMGY^(V) _(I)I G

where the presence of a different amino acid from the consensus sequence indicates a putative HBV variant. 